A disease of the eye known as macular degeneration has become one of the leading causes of blindness in adults. This disease affects the central retinal area known as the macula which affords acute vision and receives light focused by the cornea and lens. This disease can lead to a gradual or sudden loss of vision to the level of 20/200 or less. Commonly, loss of vision only affects the central retinal area of about 0.25 to 4 square millimeters and does not usually progress beyond this area, thereby leaving 95-99% of the retina unaffected. Thus, reading and driving vision can be lost but peripheral vision remains intact.
Most cases of macular degeneration are untreatable, although laser photocoagulation has been some benefit in certain instances. Telescopic systems that attach to eye glasses also have been used for many years to improve vision in patients with macular degeneration. These systems, which work by increasing the retinal image size of a given object, however, have not been very successful because they restrict the visual field to about 11.degree. so that normal activity is not possible. They are also large and bulky. Attempts have been made to increase the visual field by putting part of the telescope within the eye. A Galliean telescope is useful for this purpose and consists of a high converging objective lens and a high diverging ocular lens, which together produce a telescopic effect.
Recent publications by Charles Koester disclose that a high diverging lens can be implanted inside the eye and then high converging glasses are worn to provide a telescope having a significantly improved visual field of about 37.degree.. A similar system was earlier described by Peter Choyce, who implanted a high diverging anterior chamber lens and used high converging spectacle glasses to create telescope in patients.
While the system described by both Koester and Choyce is an improvement over the prior spectacle-attached telescopes, it nevertheless has one inherent and severe drawback. The high minus intraocular lens implanted in the patient's eye is incapable of providing a focused retinal image by itself. It can only provide a focused retinal image when combined with an external converging spectacle lens, and then, the only image possible is a magnified image of reduced visual field. The adjustment to such permanent magnification and reduced visual field is very difficult for patients since objects seem larger and thus appear closer and peripheral vision is severly restricted. Magnification may be fine for reading and other close work which use direct vision, but it is very burdensome for activities such as walking, shopping, etc., which can be comfortably carried out even with macular degeneration. Likewise, permanent reduction in peripheral vision restricts a person's activities.
Thus, there is a need for an ocular device which allows a patient to choose between magnified vision with decreased visual field, or the less acute vision normally associated with macular degeneration with unrestricted peripheral vision.